During a biological assay researchers may use a camera to capture images of cell responses during the data acquisition phase. One type of biological assay may measure the response of cardiac muscle cells (cardiomyocytes) to potential drug compounds. This type of cardiomyocyte assay may load cardiomyocyte cells with a calcium dye, add a potential drug compound, and measure, for example, the changing spectral properties (e.g., fluorescence or luminescence) of the calcium dye due to biological activity at the cardiomyocytes.
Assaying cardiomyocytes may involve monitoring changes to the concentration gradient of calcium ions across a cardiomyocyte membrane that result in changes to the membrane voltage potential for the cardiomyocyte. A cardiomyocyte assay may monitor the flux of calcium ions into and out of a cardiomyocyte using the calcium dye. The calcium dye may have spectral properties, e.g., fluorescent or luminescent properties that change in the presence of calcium ions. Accordingly, light may serve as a proxy for calcium flux.
A camera, as mentioned above, may capture images of the cardiomyocytes during the assay to monitor the changes in the light from the calcium dye. Researchers may then analyze the image data to determine the effects of potential drug compounds on the cardiomyocytes.
The camera may be capable of capturing images at a relatively high frame rate, e.g., 120 frames per second (fps). Overhead, however, may limit the effective frame rate of the camera when processing the image data.
As an example, a camera may take a 0.05 second (sec.) exposure of a biological assay sample during a 0.125 second interval period. Part of the interval period, e.g., 0.075 seconds, may be devoted to software overhead that includes image data handling and transmission. As a result, the exposure time and overhead that comprise the interval period may limit the effective frame rate of the camera to 1÷(exposure time+overhead) frames per second.
Using the example above, the effective frame rate for a 0.05 sec. exposure and 0.075 sec. overhead is 8 fps: 1÷(0.05+0.075)=I÷0.125=8 fps. Thus the overhead inhibits utilization of the camera maximum frame rate, e.g., 120 fps. Relevant biological activity, however, may occur during the overhead period—in other words, between exposures—and fail to be captured by the camera. Attempting to use the maximum frame rate despite the overhead shortens the available exposure time. A short exposure time may result in an image signal too dim to produce an adequate image of the assay sample. Accordingly, the effective frame rate of the camera may also be inhibited by the need for an exposure time long enough to produce an adequate image.
Therefore a need exists for a new approach to imaging biological assays that can take advantage of the high-speed capabilities of the imaging camera.